prefer const contructors in packages/flutter_driver (#8056)

packages/flutter_driver/lib/src/common.dart

@@ -11,7 +11,7 @@ import 'package:file/memory.dart';
 /// The file system implementation used by this library.
 ///
 /// See [useMemoryFileSystemForTesting] and [restoreFileSystem].
-FileSystem fs = new LocalFileSystem();
+FileSystem fs = const LocalFileSystem();
 
 /// Overrides the file system so it can be tested without hitting the hard
 /// drive.
@@ -21,7 +21,7 @@ void useMemoryFileSystemForTesting() {
 
 /// Restores the file system to the default local file system implementation.
 void restoreFileSystem() {
-  fs = new LocalFileSystem();
+  fs = const LocalFileSystem();
 }
 
 /// Flutter Driver test ouputs directory.

packages/flutter_driver/lib/src/driver.dart

@@ -157,7 +157,7 @@ class FlutterDriver {
         isolate.pauseEvent is! VMPauseExceptionEvent &&
         isolate.pauseEvent is! VMPauseInterruptedEvent &&
         isolate.pauseEvent is! VMResumeEvent) {
-      await new Future<Null>.delayed(new Duration(milliseconds: 300));
+      await new Future<Null>.delayed(const Duration(milliseconds: 300));
       isolate = await vm.isolates.first.loadRunnable();
     }
 

packages/flutter_driver/lib/src/timeline_summary.dart

@@ -12,7 +12,7 @@ import 'package:path/path.dart' as path;
 import 'common.dart';
 import 'timeline.dart';
 
-final JsonEncoder _prettyEncoder = new JsonEncoder.withIndent('  ');
+final JsonEncoder _prettyEncoder = const JsonEncoder.withIndent('  ');
 
 /// The maximum amount of time considered safe to spend for a frame's build
 /// phase. Anything past that is in the danger of missing the frame as 60FPS.

packages/flutter_driver/test/flutter_driver_test.dart

@@ -120,7 +120,7 @@ void main() {
     group('ByValueKey', () {
       test('restricts value types', () async {
         expect(() => find.byValueKey(null),
-            throwsA(new isInstanceOf<DriverError>()));
+            throwsA(const isInstanceOf<DriverError>()));
       });
 
       test('finds by ValueKey', () async {
@@ -140,7 +140,7 @@ void main() {
 
     group('tap', () {
       test('requires a target reference', () async {
-        expect(driver.tap(null), throwsA(new isInstanceOf<DriverError>()));
+        expect(driver.tap(null), throwsA(const isInstanceOf<DriverError>()));
       });
 
       test('sends the tap command', () async {
@@ -159,7 +159,7 @@ void main() {
 
     group('getText', () {
       test('requires a target reference', () async {
-        expect(driver.getText(null), throwsA(new isInstanceOf<DriverError>()));
+        expect(driver.getText(null), throwsA(const isInstanceOf<DriverError>()));
       });
 
       test('sends the getText command', () async {
@@ -182,7 +182,7 @@ void main() {
 
     group('waitFor', () {
       test('requires a target reference', () async {
-        expect(driver.waitFor(null), throwsA(new isInstanceOf<DriverError>()));
+        expect(driver.waitFor(null), throwsA(const isInstanceOf<DriverError>()));
       });
 
       test('sends the waitFor command', () async {
@@ -195,7 +195,7 @@ void main() {
           });
           return makeMockResponse(<String, dynamic>{});
         });
-        await driver.waitFor(find.byTooltip('foo'), timeout: new Duration(seconds: 1));
+        await driver.waitFor(find.byTooltip('foo'), timeout: const Duration(seconds: 1));
       });
     });
 
@@ -289,7 +289,7 @@ void main() {
           return new Completer<Map<String, dynamic>>().future;
         });
         try {
-          await driver.waitFor(find.byTooltip('foo'), timeout: new Duration(milliseconds: 100));
+          await driver.waitFor(find.byTooltip('foo'), timeout: const Duration(milliseconds: 100));
           fail('expected an exception');
         } catch(error) {
           expect(error is DriverError, isTrue);

packages/flutter_driver/test/src/retry_test.dart

@@ -38,13 +38,13 @@ void main() {
                 return retryCount;
               }
             },
-            new Duration(milliseconds: 30),
-            new Duration(milliseconds: 10)
+            const Duration(milliseconds: 30),
+            const Duration(milliseconds: 10)
           ),
           completion(2)
         );
 
-        fakeAsync.elapse(new Duration(milliseconds: 50));
+        fakeAsync.elapse(const Duration(milliseconds: 50));
 
         // Check that we didn't retry more times than necessary
         expect(retryCount, 2);
@@ -60,14 +60,14 @@ void main() {
           // that `retry` keeps trying until the counter reaches 2.
           retry(
             () async => retryCount++,
-            new Duration(milliseconds: 30),
-            new Duration(milliseconds: 10),
+            const Duration(milliseconds: 30),
+            const Duration(milliseconds: 10),
             predicate: (int value) => value == 2
           ),
           completion(2)
         );
 
-        fakeAsync.elapse(new Duration(milliseconds: 50));
+        fakeAsync.elapse(const Duration(milliseconds: 50));
       });
     });
 
@@ -83,15 +83,15 @@ void main() {
             retryCount++;
             throw 'error';
           },
-          new Duration(milliseconds: 7),
-          new Duration(milliseconds: 2)
+          const Duration(milliseconds: 7),
+          const Duration(milliseconds: 2)
         ).catchError((dynamic error, dynamic stackTrace) {
           timedOut = true;
           lastError = error;
           lastStackTrace = stackTrace;
         });
 
-        fakeAsync.elapse(new Duration(milliseconds: 10));
+        fakeAsync.elapse(const Duration(milliseconds: 10));
 
         expect(timedOut, isTrue);
         expect(lastError, 'error');